The present invention relates to a head arm of a magnetic disk device, and more particularly, to a head arm of a magnetic disk device having one or more features for reducing vibrations attributable to turbulence of the air flow generated with the rotation of the magnetic disk.
Currently, a commonly used hard disk device used for an internal or external storage unit or the like has a CSS (contact start stop) system in which the magnetic disk medium and the magnetic head are in contact with each other at the time of activation. In this type of hard disk device, the magnetic head mounted at the forward end of the head arm through a suspension floats due to the air flow generated with rotation of the magnetic disk.
FIG. 11 is a perspective view schematically showing a conventional magnetic disk device, in which a magnetic disk 43 is mounted on a spindle motor 42 fixed on a housing 41, and is adapted to be rotated at a predetermined rotational speed by the spindle motor 42. A magnetic head 46 for reading/writing the magnetic information recorded on the magnetic disk 43 is suspended on a suspension 45 mounted at the forward end of the head arm 44, and floats due to the air flow generated with the rotation of the magnetic disk 43.
The head arm 44 is rotatably mounted on a rotary shaft 47 and is adapted to swing in the direction along the diameter of the magnetic disk 43 by an actuator making up a head arm drive motor 49. In this case, the access rate to the data written in the magnetic disk 43 is determined by the rotational speed of the magnetic disk 43 and the moving speed of the head arm 44. For achieving a faster access, therefore, the rotational speed of the magnetic disk 43 and the moving speed of the head arm 44 can be increased.
With the conventional head arm 44, in order to improve the access rate, the forward end portion nearer to the suspension 45 is formed with a substantially rectangular weight-reducing aperture 48 about 6 mm wide and about 20 mm long, to reduce the moment of inertia of the head arm 44. The air flow caused by rotation of the magnetic disk 43, however, generates an air eddy in the weight-reducing aperture 48 formed in the head arm 44. This air eddy provides a source of vibration of the head arm 44, thereby leading to the problem of reduced positioning accuracy of the magnetic head 46. This situation will be explained with reference to FIG. 12.
FIG. 12(a) also shows a conventional head arm, and FIG. 12(b) shows the head arm interposed between two magnetic disks 50, 51. An air eddy 53 is generated in the weight-reducing aperture 48 formed in the head arm 44, and vibrates the head arm 44.
The conventional head arm 44 has a rectangular sectional shape. The phenomenon of flow separation occurs, therefore, downstream of the head arm 44, thereby generating an air eddy. With this air eddy as a vibration source of the head arm 44, the problem of reduced positional accuracy of the magnetic head 46 is posed. This situation will be explained with reference to FIG. 13.
FIG. 13(a) shows another conventional head arm, and FIG. 13(b) shows the head arm interposed between two magnetic disks 50, 51. Air eddies 54 are generated in the neighborhood of the downstream end portion of the head arm 44, and vibrates the head arm 44.
FIG. 13(c) shows the result of simulation of the air flow 52 in the neighborhood of the downstream end of the head arm 44 as viewed along the direction indicated by the arrow in FIG. 13(a). To simplify the illustration, the suspension and the magnetic head are not shown. It can be seen that the air flow 52 is disturbed and air eddies 54 are generated in the neighborhood of the downstream end of the head arm 44.
In the neighborhood of the central portion along the thickness of the portion near the head arm 44, the air flow 52 from the root or axis of the head arm 44 toward the forward end thereof is generated with rotation of the magnetic disk 43. The forward end portion of the conventional head arm 44 is arcuate. Therefore, the air flow 52 is separated and an air eddy 55 is generated at the forward end portion, as seen in FIG. 14. This air eddy 55 is a vibration source of the head arm 44, thereby leading to the problem that the positional accuracy of the magnetic head is reduced.
In the conventional magnetic disk device, both the rotational speed and the velocity of the air flow generated by rotation of the magnetic disk are low. Therefore, vibration has not posed a serious problem. For this reason, neither the shape of the weight-reducing aperture of the head arm nor the sectional shape of the head arm has been taken into consideration specifically in the design stage.
In recent years, however, in order to achieve a higher access rate, the rotational speed of the magnetic disk has been increased, which in turn has increased the velocity of the air flow generated by rotation of the magnetic disk. As a result, suppression of vibration of the head arm caused by pneumatic force, which has conventionally been ignored, has come to pose a serious problem.
Specifically, with the recent increase in recording density, an improved positioning accuracy of the magnetic head has posed a crucial problem. To obviate this problem, it is necessary not only to improve the head positioning control system but also to reduce the disturbance of the pneumatic force by the head arm and the adverse effect of the disturbance on the positioning accuracy of the magnetic head.
Accordingly, an object of the present invention is to reduce the turbulence of the air flow around the head arm.